With vcgencmd no longer working, determine the power status of a connected display with xrandr

The vcgencmd command returned a “0” or “1” depending on the connected monitor being off or on, but unfortunately, this is no longer working with Raspberry Pi OS Bullseye or Bookworm.

I tried tvservice -s, kmsprint -m, and ddcutil detect but neither was working.

So, it was time to see if xrandr would contain any useful function to achieve something to that effect.

Using

DISPLAY=:0.0 xrandr

you get information about connected displays. But it is almost the same information, regardless of whether the display is powered on or off. But on closer inspection, there were some distinct differences:

On the left is the information when powered on, and the power-off data on the right. When a display is powered on, the resolution information is given after “HDMI-1 connected primary”.

So, I wrote a little Python test script parsing the output and checking if the

3840x2160+0+0

was included.

#!/usr/bin/python3

import subprocess

def is_hdmi1_connected(display=":0.0"):
    try:
        # Run the xrandr command and capture its output
        command = f"DISPLAY={display} xrandr"
        output = subprocess.check_output(command, shell=True).decode('utf-8')

        # Check if "HDMI-1 connected primary 3840x2160" is in the output and marked as "connected"
        if 'HDMI-1 connected primary 3840x2160' in output:
            return True
        else:
            return False
    except subprocess.CalledProcessError:
        # Handle any errors that may occur
        return False

if is_hdmi1_connected():
    print("Display is on.")
else:
    print("Display is off.")

Depending on your connected display, you must change the resolution to make it work for you.

Thank you for your support and motivation.